All current aircraft manufacturing techniques require structural shimming at interface surfaces between structural components, such as frames, stringers, spars, etc. where tolerance buildup prevents net-line fits. The current technique is to hand-cut laminated shim material to create a shim sized to fill the gap between the interfacing surfaces. After shim beveling is completed, the shim profile is trimmed with an aircraft shears. Because this technique is timeconsuming and labor-intensive, it is expensive. Another disadvantage of this technique is its dependence on the skill of the person that manufactures the shim, which varies from individual to individual.
Various proposals have been made to overcome the disadvantages of the foregoing technique. One proposal has been to form shim master molds and use the molds to create master shims. While useful in some situations, this technique is not useful in others, particularly where the gap to be filled by the shim is very narrow. Further, master mold shims have to be hand-tailored for each individual interface situation, which is undesirable because it is expensive and creates a large inventory of master molds.
Recently, a probe for use in determining the thickness of an interface gap, i.e., a gap between two facing components, has been developed. The probe is described in U.S. Pat. No. 4,649,752 entitled "Shim Gap Probe," which is assigned to the assignee of the present invention. The subject matter of U.S. Pat. No. 4,649,752 is incorporated herein by reference. The probe described in U.S. Pat. No. 4,649,752 includes a wavespring formed in one end of a thin, flat, elongate piece of resilient material, such as spring steel. The wavespring includes at least three sinusoidal waves having a peak-to-peak separation that is greater than the maximum thickness of the gaps to be measured. Mounted on the wavespring, at the bottom of the concave depressions formed by each of the sinusoids, are strain gauge sensors. Each depression supports at least two strain sensors oriented to sense the radial and circumferential strain applied to the wavespring when the wavespring is positioned in an interface gap. The strain sensors in each depression are combined to form strain gauge bridges. In a conventional manner, the strain sensors control the magnitude of electric signal flow through the bridges to provide a measure that is indicative of the compression of the wavespring and, thus, the thickness of the gap. The use of at least three sinusoids provides two-dimensional taper, as well as thickness information since three precisely positioned, spaced apart thickness measurements are created.
The present invention is directed to an automatic shim manufacturing system that utilizes the shim gap information generated by a shim gap probe, preferably a shim gap probe of the type described in U.S. Pat. No. 4,649,752, to control the manufacturing of shims and, thereby, avoid the disadvantages associated with the hand manufacture and master mold techniques discussed above.